1. Field of the Invention
The present invention relates to a magnetic cell and a magnetic memory.
2. Related Art
For controlling magnetizing direction of a magnetic body, a method for applying magnetic field on the magnetic body has been conventionally employed. For example, in a hard disc drive, a magnetizing direction of a medium is inverted for performing writing by magnetic field generated from a recording head. In a solid magnetic memory, a current magnetic field generated due to current flowing in a wire provided near a magnetoresistance effect element is applied to a memory cell, so that control on a magnetizing direction of the memory cell is performed. The magnetizing direction controls made by these external magnetic fields are said to be an old technique and an established art.
On the other hand, according to advance of the recent nano-technology, magnetic material particle are made further fine, which results in need for local magnetizing control with nano-scale. However, since the magnetic field is fundamentally provided with a property of expanding in space, it is difficult to conduct localization. According to further fineness of a bit or a memory cell in size, when a specific bit or memory cell is selected and its magnetizing direction is controlled, such a problem about “cross talk” where magnetic field influences an adjacent bit or memory cell occurs noticeably. When a magnetic field generating source is made small for achieving localization of magnetic field, there arises another problem that a sufficient generated magnetic field can not be obtained.
In recent year, “magnetization reversing of current direct driving type” where magnetization reversing takes place due to current flowing in a magnetic body has been found (for example, refer to F. J. Albert, et al., Appl. Phys. Lett. 77, 3809 (2000)).
The magnetization reversing due to current flow is a phenomenon where reversing of magnetization is caused by transmitting/operating an angular momentum of spin-polarized electrons generated when spin-polarized current passes through a magnetic body on an angular momentum of a magnetic body to be magnetization-reversed. Direct serving on a magnetic body of nano-scale is made possible by utilizing the phenomenon, so that recording on a further fine magnetic body becomes possible.
In the conventional magnetic element utilizing magnetization reversing of current direct driving type, methods where a laminated magnetic body film is directly etched by such a process as a direct milling or a RIE (Reactive Ion Etching) are used. In these direct etching processes, however, when a much fine element with a size of 10 nm or less is etched, there is a problem that it is difficult to form such an element having a high developing rate of MR characteristics without fluctuation due to damage during the etching process or re-adhesion of etched material. There is a problem that, for forming a small element pillar, an element itself must be prevented from falling down.
In order to form a fine element without using an etching process while preventing the element from falling down, there is such a trial that fine holes are formed in an insulator and formation is conducted by embedding (for example, refer to J. Z. Sun, et al., Appl. Phys. Lett. 81, 2202 (2002)). In the trial, however, there is a problem that a film forming apparatus is required for a high directivity and a fine element can not be manufactured with the embedding structure when a structure film thickness of a magnetic body film portion performing current direct driving is increased.